(a) Field of the Invention
The present invention relates to a small-sized pump and, more particularly, to a small-sized pump which makes it easy to assemble the pump and motor into one unit and which is especially suitable for the use with a simplified-type sphygmomanometer and the like.
(b) Description of the Prior Art
In recent years, simplified-type sphygmomanometers by which people in general can measure the blood pressure by themselves are put on the market. The above-mentioned type of sphygmomanometers employ a pump which is driven by a small-sized and powerful pump.
The above-mentioned kind of known pumps are constructed as shown in FIGS. 1 and 2. That is, FIG. 1 shows a side view and FIG. 2 shows a front view of said known pump. In said figures, numeral 1 designates a base, numeral 2 designates a small-sized DC motor, numeral 3 designates an output shaft of the motor 2, numeral 4 designates an eccentric cam which is fixed to the output shaft 3, numeral 5 designates a drive shaft which is fixed to the eccentric cam in a position eccentric from the output shaft 3, numeral 6 designates a bearing which is slidably fitted to the drive shaft 5, numeral 7 designates a rod which is fixed to the bearing 6, and numeral 8 designates a diaphragm unit which is fixed to the base 1 and which constitutes the pump together with a part of the base 1. The diaphragm unit 8 is constructed as illustrated by the sectional view shown in FIG. 3. That is, a diaphragm 10 is fixed to a case 9, and the central portion of the diaphragm 10 is fixed to the end of the rod 7.
The known small-sized pump constructed as mentioned in the above operates as described below. That is, when the motor 2 is energized and started, the output shaft 3 rotates and, therefore, the drive shaft 5 revolves round the output shaft 3 so as to make the rod 7 move upward and downward. As the rod 7 moves upward and downward as mentioned in the above, the central portion of the diaphragm 10 in the diaphragm 8 performs reciprocating motion in the substantially vertical direction and, consequently, the pumping action is performed.
In case of said known pump, the height of the pump becomes large because a long rod is used and, moreover, the motor and diaphragm unit are arranged at positions distant from each other. Therefore, the pump as a whole becomes large, and it is difficult to make the pump small in size.
If the rod is made short, it becomes difficult to make the diaphragm perform the reciprocating motion. As a result, the diaphragm is deformed forcibly, and the power consumption becomes large.
Moreover, as the diaphragm unit 8 is so constructed that the diaphragm 10 has a comparatively flat shape and the circumferential portion of the diaphragm 10 is fixed to the case 9, the portion 10a of the diaphragm 10 swells as shown by the chain lines in FIG. 3 when the rod comes down and the internal pressure increases and, consequently, it is impossible to obtain sufficient pressure increase.